1. Field of the Invention
The invention relates to a surgical instrument for driving elongated pins or wires. In particular, the invention relates to a pin or wire driver having a collet mechanism which permits the pin or wire to be selectively released and engaged in order to be repositioned. The mechanism also permits automatic sizing of the collet to accept a range of pin/wire diameters. More particularly, the invention relates to a pin or wire driver collet adjustment mechanism suitable for one-handed operation.
2. Description of the Prior Art
Powered surgical instruments for driving elongated pins or wires are well known. While pins usually have larger diameters than wires, for purposes of this description, the terms "pins" and "wires" will be considered interchangeable. For simplicity, the term wire driver will be used to mean a driver for driving pins as well as wires or other similar, wire-like elongated devices (i.e. relatively rigid shafts which may or may not have pointed or drill tips and are usually, but not necessarily, made of metal such as stainless steel, nitinol, etc.) . Such instruments generally comprise a handpiece adapted to drive a cannulated drive shaft through which a wire may be passed. Since the wire to be driven may be relatively long, the drive shaft extends entirely through the handpiece from a proximal end to a distal end and is provided with a collet/chuck mechanism in order to selectively secure the wire to the drive shaft. The instrument is used to turn the drive shaft which, consequently, turns the wire in order to advance the wire extending from the distal end of the drive shaft into a bone or other structure at a surgical work site. Depending upon the desired penetration depth and other factors, the length of wire extending from the distal end of the drive shaft may need to be adjusted in order to optimize control of the wire. The wire's extended length is usually relatively short as the wire is first driven into the surgical work site and then, if additional penetration is desired, the grip on the wire is somehow overcome or released so the wire may be repositioned within the drive shaft and driven further into the surgical work site. Often, the collet mechanism is similar to a one-way clutch which permits the wire to be pulled out of the handpiece distally, but does not permit it to be pushed proximally. It will be noted that once the wire is sufficiently embedded at the surgical work site in a bone, for example, the distal end of the wire will be held in place by the bone. That is, in such a case there is no need for a surgeon to grasp the wire because the collet mechanism allows the wire to "slip" when the handpiece moves proximally along the wire (and the wire moves distally). The surgeon simply needs to move the handpiece relative to the wire until the desired length of wire extends from the drive shaft.
Some prior art wire drivers are provided with collet mechanisms which frictionally engage the wire at all times to a certain degree. This is necessary as a practical matter so that the wire does not simply fall out of the wire driver as the latter is manipulated during use. Other prior art wire drivers enable the wire to slide more freely. One example of such a prior art wire driver is described in U.S. Pat. No. 4,736,742 (Alexson et al.) which shows a wire driver attachment releasably attached to a gas operated handpiece having a pair of parallel output drive shafts, one of which is cannulated. The handpiece has a pistol-grip and a trigger for activating its drive shafts. The wire driver attachment fits on the handpiece in such a way as to align the cannulated output shaft with the wire being driven. A pivotable, spring-loaded lever is situated on the wire driver attachment and is movable between a release position, spaced away from the pistol-grip handle, and an engage position adjacent the handle. The action of the lever controls a cam surface in the attachment by moving it to selectively release or engage a plurality of locking balls circumferentially arranged around the wire being driven. The locking balls and associated cam surfaces are components of a threaded, cylindrical chuck which is adjustable by a user, using a second hand, so the wire can be frictionally held by the locking balls. However, this adjustment is usually made in practice just to size the collet for the wire. That is, in actual use the locking balls are adjusted close to but not simultaneously contacting the wire and cam surface. The wire may then be normally fully released so that it could fall out of the driver or the mechanism may be adjusted so the wire can be slid longitudinally through the chuck with the lever in the release position (i.e. its normally biased position). In either case, the wire would be tightly engaged by the locking balls when the lever is in the engage position. The handpiece is activated by a user pulling an activating trigger while moving the lever to the engage position. When pressure is removed from the lever, it returns to its release (i.e. lightly gripping or sliding) position in which the device allows longitudinal movement of the wire relative to the chuck. In any case, the wire driver shown in this patent requires a two-handed operation for any adjustment of the cylindrical part which sizes the mechanism to match the wire then in use.
Another known wire driver assembly utilizes a collet mechanism based on a plurality of gripper discs circumferentially arranged about a wire to be driven. Such a device is available from Zimmer, Inc., Warsaw, Ind. (an affiliate of the assignee of this invention) in the form of a lever-less pin driver assembly more particularly described below by reference to FIG. 6.
The aforementioned devices as well as other conventional wire drivers are designed and adjusted to hold wires in position so they will not move or fall out of the collet under their own weight. As mentioned, this is necessary as a practical matter to prevent the wires from falling out of the handpiece. However, this produces a disadvantage in that once the wire has been initially inserted into the driver, minor adjustments of the wire position in the collet are not easily achievable. The surgeon must either use his/her other hand or the assistance of another person in order to achieve the precise wire position desired. Since the surgeon's other hand may already be occupied, this is an obvious limitation which may adversely affect the efficiency of the surgical procedure.
It has been found that it would be desirable to enable a surgeon to simply rest the distal tip of the wire against a sterile surface (such as a surgical drape, etc.) and, with the hand holding the driver, release the wire so it can fall under its own weight. This would enable the surgeon to move the driver up or down the wire without the assistance of another person and without having to grasp the wire, while also having the driver normally maintain a light grip on the wire preventing it from falling out. The same mechanism enables the wire driver to automatically adjust its collet size to accept a wide range of wire diameters.
Accordingly, it is an object of this invention to produce a wire driver collet mechanism which enables the wire to be selectively repositioned or engaged.
It is a further object of this invention to produce a wire driver collet mechanism which enables the wire to be selectively repositioned under its own weight.
It is another object of this invention to produce a wire driver collet mechanism, for a wire driver handpiece, in which the wire may be selectively repositioned easily with a one-handed operation utilizing the same hand which holds the wire driver handpiece. That is, it is also an object of this invention to produce a wire driver which enables a user to selectively reposition the wire driver on the wire while using only one hand to hold the driver and control the collet holding the wire.
It is another object of this invention to enable this to be done with a lever-operated wire driver attachment since that is a structure commonly used in similar devices.
It is an additional object of this invention to produce a wire driver collet mechanism which automatically adjusts to accept a wide range of wire diameters.